In order to improve the reactor safety and its dynamic properties, as well as to reduce consequences of start-up reactivity accidents, it is feasible to implement engineering measures to prevent “blind” start-up, because in subcritical reactor the neutron flux is the only and the most important variable parameter at reactivity rise. The controlled start-up means the possibility to measure the neutron flux in the reactor core depending on the position of standard control equipment compensating rods.
The amount of neutrons generated in the core as a result of spontaneous uranium fission (˜2 103 n/s), is not sufficient to provide a controlled neutron flux in measuring chambers during the start.
The reactor subcriticalilty and power control is one of the most important nuclear safety tasks. In order to provide controlled reactor start-up, it is essential to ensure that the core neutron power is consistent with the response of ionization chambers monitoring the neutron flux which are located in a specific area near the core.
In order to ensure the control, the neutron flux in a subcritical reactor shall be increased significantly, or the start-up equipment response shall be increased accordingly. The most appropriate solution of the reliable power control problem of reactors (in the initial subcritical state) equipped with pulse start-up equipment is the allocation of neutron sources in the core.
Neutron sources designed as cluster assemblies are currently in use. The assembly includes two types of rods: rods with antimony filling, and rods with a hot-pressed beryllium bed.
Such designs are very large and occupy a considerable area in the core.
Neutron sources based on antimony-beryllium composition pellets enclosed in a single housing are currently in use. At present, such neutron source design is used at naval nuclear facilities.
The shortage of this design is potential antimony melting during the source manufacture and operation, resulting in the stratification of the antimony-beryllium composition and source efficiency degradation.
A monoenergetic neutron source is currently in use, disclosed in Patent RU No. 1762676, MPK G21G4/00 of Aug. 30, 1994. This neutron source is designed as radioactive antimony in a beryllium enclosure which is placed in the iron layer, with varying thickness of the beryllium and ferrum layers, which thickness is determined by the calculated ratios.
The device contains a photon source, cylinder-shaped antimony, a photoneutron source, beryllium shaped as a cylindric tube, a neutron filter, barrel-shaped ferrum, in which an antimony-beryllium system is placed, and then capped with an iron plug.
The shortage of this design is also potential antimony melting during the source manufacture and operation, resulting in the stratification of the antimony-beryllium composition and source efficiency degradation.